How important is life assessment for plastic moulds?

Plastic moulds, as repeated consumables, can have an impact on the quality production or processing of the entire product line if defects or failure problems arise, especially for mass produced products, which can lead to losses that cannot be assessed. When plastic moulds leave the factory, a life assessment is done on them before they fail. Byrne Testing can provide services such as normal life assessment, first life assessment, mould repair life assessment and total life assessment for plastic moulds.

By life time we mean the number of times the mould can be produced (number of stamps, number of moulds) while ensuring the quality of the parts. Plastic moulds as consumable, items must be repeatedly ground and replaced until the main part of the mould has been replaced by the total number of qualified parts formed. For moulds that generate faults, there are abnormal faults and normal faults. Abnormal failure means that the mould will not work unless the life expectancy at industrial levels is reached. Early forms of damage include plastic deformation, fracture and severe localised wear. Normal failure means that the mould is used for mass production and is plastically deformed due to slow or uniform wear or fatigue failure until it is no longer able to operate. Life assessment is about analysing the failure mechanism of plastics before they fail and thus deriving the service time.

I. Plastic mould failure mechanisms

It can be summarised into three types: wear, fracture and plastic deformation.

1, wear and tear failure mechanism:

As the mould advances, it comes into contact with the forming blank to produce relative movement. Contact surface due to the relative movement of the surface and the gradual loss of material phenomenon called wear. Wear defects can be divided into fatigue wear, cavitation wear, erosion wear, abrasion wear, etc.. These are the reasons for the failure of plastic moulds.

2, fracture failure mechanism:

Fracture failure refers to the plastic mould produced by the crack is larger or separated into two parts, and lead to processing capacity to reduce the phenomenon. Fracture can be divided into plastic fracture and brittle fracture. Most of the mould materials are medium to high strength steel, fracture form is mostly brittle fracture. Brittle fracture is also divided into one-time fracture and fatigue fracture.

3, plastic deformation failure mechanism:

Very often, plastic moulds will be unevenly subjected to large stresses during operation. If the temperature under the yield limit is exceeded, the mould will produce lattice, grain boundary slip phenomenon, resulting in plastic deformation, shape or size change, thus can not be repaired and rework. The fracture modes of plastic deformation are coarsening, bending, swelling, collapse, etc. The plastic deformation of a mould is in fact the yielding process of the mould material. Whether plastic deformation occurs or not, the mechanical load and the high temperature strength of the mould have a decisive influence.

It is worth mentioning that in the production and processing of plastic products, plastic moulds can cause defects in the product forming process for various reasons. If not all moulded or moulded products are too small, manpower is required to remove residual plastic products that have stuck to the pallet mould. Press the iron and bevel downwards to strike the mould to remove residual plastic product from the mould. Scratching, denting and other impacts are inevitable in mould damage during the curling process. This is partly responsible for the reduced life of plastic moulds. So to avoid failing a plastic product test report, a plastic mould life assessment is naturally essential.